1. Field of the Invention
This invention relates to a hydrostatic drive system with a consumer, such as a hydraulic motor, located in an open circuit. Associated with the consumer is at least one pressure limiting device that can be actuated in the braking phase for generation of a braking pressure on the discharge side of the consumer. The braking pressure can change from a minimum response pressure to an increase in the response pressure. A feeder device provides a feed of pressure fluid into the admission side of the consumer.
2. Technical Considerations
Drive systems of this type are used, for example, as slewing gear drives for mobile machines, such as excavators. To decelerate the consumer, a control valve that controls the consumer is actuated into a neutral position in which the pressure fluid lines leading to the consumer are blocked. As a result of the inertia of masses in movement of the revolving superstructure of the excavator that is driven by the slewing gear, the consumer continues to be driven during the braking phase. As a result of which, the pressure conditions at the consumer are reversed. A braking pressure then accumulates in the discharge side of the consumer, which is protected by means of a pressure limiting device.
The pressure limiting device is provided with a pressure increase circuit. During the braking phase, the pressure limiting device is pressurized within a defined length of time from a minimum response pressure to a maximum response pressure. During this pressure increase, the response pressure of the pressure limiting device therefore increases, as does the braking pressure that decelerates the consumer. The play that results from manufacturing tolerances in the gear train of mechanical gearing associated with the slewing gear drive, with a shift of the gearing at the beginning of the braking phase, is thereby passed through at the minimum response pressure. As a result of which, a smooth deceleration of the slewing gear is achieved. As a result of the ability to increase the pressure in the pressure limiting device, a smooth and gentle deceleration response of the drive system is therefore achieved.
To prevent cavitation on the admission side of the consumer during the deceleration phase, a feeder device is also required which, by means of feeder valves, makes it possible to feed pressure fluid into the admission side of the consumer from the reservoir or from the discharge side of the consumer.
However, a drive system of this type with pressure limiting devices in which the pressure can be increased and a feeder device that is formed by additional feed valves requires a great deal of construction and manufacturing effort and expense on account of the locations in which the system must be installed and the lines and conduits required for the pressure limiting devices and the feeder devices.
Therefore, it is an object of the invention to provide a hydrostatic drive system of the general type described above but that requires relatively little construction and manufacturing effort and expense.